 
strict digraph loopgraph {
    rankdir=BT;
    node[color=blue, fillcolor=lightblue, style=filled];

    L1->L4->L8;
    L2->L4->L6->L8; L6->L9;
    L3->L5->L7->L9;
    L1->L7;
    node Rank0;
    node Rank1;
    node Rank2;

    {rank=same; Rank0 L1 L2 L3}
    {rank=same; Rank1 L4 L5}
    {rank=same; Rank2 L6 L7}
    

}